The day before an important ride like a long ride, I have to be careful as to what I eat.
I will notice right away if I'm sluggish in the early morning. Once I get on the bike, I will know in the first mile as to how I feel. Sometimes that feeling will last a while until I get the body out of the slump. Other times, I feel great from the get-go.
I try to stay away from a heavy, greasy meal. Even sushi with the soy sauce is not good for me. Nor is the tempura because of its fried nature. I do crave Inari Sushi which is somewhat fried tofu skins with white rice. The Vietnamese Pho is ok, so long as I don't eat the beef but use it as flavoring for the broth. I peel off the leaves from the stalk and dump in the veggies into the broth, squeeze the hot sauce in and "chow-down" the noodle soup. I hardly drink the broth...
What my body likes is vegetables and fruit. I try to drink a lot of water throughout the day and even in the evening before sleep. I admit that I pee the water at night but that's ok because its clear and in the morning I feel less sluggish. Try it, eat very little for dinner, but maybe just some fruit and vegetable and drink. Next morning you actually feel better.